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Full text of "Alaskan glacier studies of the National Geographic Society in the Yakutat Bay, Prince William Sound and lower Copper River regions"

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92                                 ALASKAN GLACIER STUDIES
being overturned are easily accounted for by normal slumping of the morainic soil, accentuated here, perhaps, by the continued development of the ridge form of the glacier through ablation.
The facts observed force Us to the conclusion that Black Glacier has experienced no notable advance under the impulse of earthquake shaking. This does not, of course,, imply that there has been no change as a result of the earthquake, for in the upper portion there may have been an advance and breaking of such slight proportions that it was not communicated to the lower portion. Possibly the small area of crevassing a little more than a mile from the terminus is a relic of such an advance.
The contrast between Black and Galiano Glacier in this respect is notable, and it ia this contrast which to us constitutes the most interesting feature of the Black Glacier. The neighboring Galiano Glacier supplies' unquestionable proof of a great advance and breaking, while Black Glacier furnishes equally convincing proof of the absence of such advance and breaking; yet both receive their snow supplies from the same earthquake-shaken area. No other reason for this difference appears than the difference in size of the glaciers; and, of course, the related difference in extent of supply area. It must be concluded that there was not a sufficient amount of unstable snow and ice available in the supply ground of Black Glacier to give the impulse necessary for advance and breakage down to the glacier terminus. It may also be true that the narrow, and perhaps, thin, ridge of ice that forms the lower Black Glacier was not a large enough mass of ice to transmit the thrust. This could only be true, though, if the thrust itself was weak; for a strong thrust would have broken and pushed forward even a rigid ice body that stood in the way. In 1905 it seemed to us a possibility, though not very probable, that the impulse of earthquake advance in the case of this glacier has for some reason been retarded and that its effects would be noted in later years. We accordingly examined it again in 1906 and in 1909, but could see no change. In 1910 and 1918 there waa no change that was visible from Yakutat Bay. That an advance could be longer delayed seems inconceivable in a glacier of such small size, and in view of the notable advance of so many other larger glaciers. We therefore conclude that not only has there been no -notable advance up to 1918, but that no future advance of the Black Glacier is to be expected as a result of the earthquakes of 1899.